Animals can respond to climate change in a variety of ways. They can move to a habitat more like the one they’re used to. They can adapt their physiology or behavior to the new conditions they’re experiencing. Or they can fail to do either, which might lead to extirpation or extinction.

Salamanders in the southern Appalachians are taking that second route — they’re changing their body size and getting smaller, report Karen Lips of the University of Maryland, College Park and colleagues March 25 in Global Change Biology.

Amphibians are considered vulnerable to environmental changes because they’re always in need of moisture and they’re cold-blooded (the ambient temperature directly affects their body temperature). Woodland salamanders in the genus Plethodon are even more sensitive because these lungless, terrestrial animals can only take in water and exchange oxygen and carbon dioxide through their skin. These salamanders were the target of the new study.

Lips and colleagues began in 2011 and 2012 by collecting representatives of a couple hundred populations of Appalachian woodland salamanders found at 85 sites in the mountains. The researchers then compared the sizes of these salamanders to museum specimens collected in the same regions from 1950 to 1996.

The change in body size was associated with change in the salamanders’ environment. In places where it got hotter and drier, salamanders shrunk more. Those areas tended to be in the southern Appalachians.

The degree and speed of change was so large and rapid, though, that “these changes represent some of the fastest responses to environmental perturbations ever recorded,” the researchers write.

Why would warm, dry conditions affect the size of a salamander? The amphibians speed up their metabolism as their body temperature rises. The research team calculated that the salamanders of today have to burn 7 to 8 percent more energy to reach the same activity level as salamanders did decades ago.

The consequences of the change in body size aren’t yet known. But body size is related to a host of life characteristics, including diet, activity patterns, foraging behavior, growth rates, reproduction, territoriality, competition and predation. Being smaller may help the amphibians adapt to a warmer, drier world, or it could set them up for as-yet-unknown problems some time in the future.